A, rate of ATP consumption per volume; B, isometric force per cross-sectional area; C, tension cost. BW, body weight; LV, left ventricular trabeculae; RV, right ventricular trabeculae. Regression lines shown: LV: ATPase activity per volume = (0.21 ± 0.02) - (14.0 ± 2.3) × 10−5× BW (r = 0.65; P < 0.001), force per cross-sectional area = (35.4 ± 4.9) + (14.0 ± 7.6) × 10−3× BW (r = 0.27), tension cost = (5.65 ± 0.35) - (4.4 ± 0.6) × 10−3× BW (r = 0.78; P < 0.001). RV: ATPase activity per volume = (0.16 ± 0.02) - (8.2 ± 2.7) × 10−5× BW (r = 0.47; P < 0.001), force per cross-sectional area = (34.5 ± 4.5) + (6.8 ± 6.9) × 10−3× BW (r = 0.17), tension cost = (4.44 ± 0.27) - (2.6 ± 0.4) × 10−3× BW (r = 0.74; P < 0.001).